Rotary shear valve assemblies are often used in HPLC Analytical, Invitro Diagnostics (IVD) and DNA Sequencing machines. These valve assemblies are characterized by relatively long life and high precision fluid delivery. Many rotary valve assemblies are driven by stepper motors which are used for positioning a grooved rotor device to multiple locations on a stator device. Rotor and stator face seal components are manufactured of chemically resistant plastic materials such as PEEK, PFA, MFA, and UHMWPE. Additionally, chemical inertness may be achieved through use of ceramic rotor and stator face seal materials such as alumina and zirconia with the added benefit of exceptional long life and low wear.
Shear valve assemblies, traditionally manufactured using expensive machining methods, can be produced by means of low cost injection molding or die casting. Such parts include sun, planet and ring gears and housings containing these components.
One of the most expensive components to manufacture is the threaded stator. The stator consists of many features including ¼-28 UNF and 6-40 UNF threads for tubing connections, ferrule interfaces, and flat surfaces subjected to compression loads to seal against mating parts, all of which significantly increase part cost. Close tolerance features such as flatness and surface roughness are achieved by secondary operations such as polishing and machine lapping as well hand lapping. Other critical features include ports and through holes. Port dimensions are held to tight tolerances and surface finish in order to effectively seal under pressure when tubing is installed. Through holes are generally specified in sizes ranging from as large as 0.060 inches in diameter to as small as 0.006 inches. Also, it is desirable for valve designs to minimize the bolt circle of through holes in order to minimize contact sealing area and maximize system pressure. Smaller bolt circles are obtained by specifying angled rather than straight through holes. Often not only are holes machined at one angle but many are machined at compound angles. While most stators consist of 5 ports to 11 ports, some are now in production with as many 25 ports and 25 through holes. Rising stator cost can also be attributed to requirements for advanced high performance polymers such as PEEK and FEP to produce superior chemical resistance. Easily one can understand why the stator is among the most expensive valve components given its complexity and composition.
Multiple processes and techniques besides threaded stators are available to achieve fluidic connections. In the field of micro-fluidic chip design a common issue relates to the fluidic interface. Many struggle finding an efficient method of physically connecting the micro size fluidic transport channels on the chip to the macro-fluidic inlet and outlets for sample delivery and fluid output. Among the techniques being used is acrylic solvent bonding between a PMMA chip and PMMA union. Manually intensive techniques such as bonding usually result in inefficient time consumption and increased cost which are not appropriate for large scale production. Another technique is press fitting a needle into PDMS material which requires maintaining sufficient compression. However, the needle can damage the PDMS material causing undesirable leakage. Another option requires an adhesive ring bonded to PDMS. However, some users report poor adhesion to untreated PDMS and working pressures of 30 to 50 psi. Moreover, because of the adhesive ring, the product is a single use connection and not reusable. Alternatively, magnetic coupling is a unique, clean and inexpensive method incorporating a rubber cup which is compression sealed between two magnets and also seals around tubing. Many other variations of bonding, needle insertion and coupling have been tried and tested but none have achieved widespread success.
Most if not all fittings in the field of DNA Sequencing, Invitro Diagnostics (IVD) and Analytical instruments use an externally threaded member and single ferrule or ferrule assembly to create a fluidic seal. Such components are required to engage into an internally threaded part with a bore for holding the ferrule.
Accordingly, it is desirable to produce a cost effective valve assembly that can interface to fluidic connections without the use of a traditional stator and eliminate threading or troublesome bonding. While this invention may find use as a fluidic connection for micro-fluidic chip applications, its primary target is designs in which fluidic channels in a rotor direct liquid to multiple positions through a disk seal where a compressive force is applied to seal a disk surface against the rotor channel. The method of producing a sealed connection between the macrofluidic environment and the microfluidic disk seal while simultaneously applying a compressive sealing pressure between the disk seal and rotor is explained in the following sections.